Fidelity Aberdeen Street Trust

It is proposed that this filing will become effective on August 30, 2018 pursuant to paragraph (a)(2) of Rule 485 at 5:30 p.m. Eastern Time.

SUBJECT TO COMPLETION. PRELIMINARY PROSPECTUS DATED JUNE 15, 2018. The information in this prospectus is not complete and may be changed. We may not sell these securities until the registration statement filed with the Securities and Exchange Commission is effective. This prospectus is not an offer to sell these securities and is not soliciting an offer to buy these securities in any state where the offer or sale is not permitted.

In this prospectus, the term “shares” (as it relates to a fund) means the class of shares offered through this prospectus.

Fidelity Freedom^® Blend Income Fund/Fidelity Freedom^® Blend Income Fund

The fund seeks high current income and, as a secondary objective, capital appreciation.

The following table describes the fees and expenses that may be incurred when you buy and hold shares of the fund.

This example helps compare the cost of investing in the fund with the cost of investing in other funds.

Let’s say, hypothetically, that the annual return for shares of the fund is 5% and that your shareholder fees and the annual operating expenses for shares of the fund are exactly as described in the fee table. This example illustrates the effect of fees and expenses, but is not meant to suggest actual or expected fees and expenses or returns, all of which may vary. For every $10,000 you invested, here’s how much you would pay in total expenses if you sell all of your shares at the end of each time period indicated:

The fund will not incur transaction costs, such as commissions, when it buys and sells shares of underlying Fidelity^® funds (or “turns over” its portfolio), but it could incur transaction costs if it were to buy and sell other types of securities directly. If the fund were to buy and sell other types of securities directly, a higher portfolio turnover rate could indicate higher transaction costs and could result in higher taxes when fund shares are held in a taxable account. Such costs, if incurred, would not be reflected in annual operating expenses or in the example and would affect the fund’s performance.

• Investing primarily in a combination of Fidelity^® domestic equity funds, international equity funds, bond funds, and short-term funds (underlying Fidelity^® funds), some of which are actively managed and others of which are passively managed, meaning they seek to provide investment results that correspond to the total return of a specific index.

• Allocating assets according to a stable neutral asset allocation strategy shown in the glide path below. FMR Co., Inc. (the Adviser) may modify the fund’s neutral asset allocations from time to time when in the interests of shareholders.

• Buying and selling futures contracts (both long and short positions) in an effort to manage cash flows efficiently, remain fully invested, or facilitate asset allocation.

• The Adviser may use an active allocation strategy to increase or decrease neutral asset class exposures reflected above by up to 10% for equity funds, bond funds and short-term funds to reflect the Adviser’s market outlook, which is primarily focused on the intermediate term. The asset allocations in the glide path above are referred to as neutral because they do not reflect any decisions made by the Adviser to overweight or underweight an asset class.

Shareholders should consider that no target date fund is intended as a complete retirement program and there is no guarantee that any single fund will provide sufficient retirement income at or through your retirement. The fund’s share price fluctuates, which means you could lose money by investing in the fund, including losses near, at or after the target retirement date.

• Asset Allocation Risk. The fund is subject to risks resulting from the Adviser’s asset allocation decisions. The selection of underlying funds and the allocation of the fund’s assets among various asset classes could cause the fund to lose value or its results to lag relevant benchmarks or other funds with similar objectives. In addition, the fund’s active asset allocation strategy may cause the fund to have a risk profile different than that portrayed above from time to time and may increase losses.

• Investing in Other Funds. The fund bears all risks of investment strategies employed by the underlying funds, including the risk that the underlying funds will not meet their investment objectives.

• Stock Market Volatility. Stock markets are volatile and can decline significantly in response to adverse issuer, political, regulatory, market, or economic developments. Different parts of the market, including different market sectors, and different types of securities can react differently to these developments.

• Interest Rate Changes. Interest rate increases can cause the price of a debt or money market security to decrease.

• Foreign Exposure. Foreign markets can be more volatile than the U.S. market due to increased risks of adverse issuer, political, regulatory, market, or economic developments and can perform differently from the U.S. market.

• Industry Exposure. Market conditions, interest rates, and economic, regulatory, or financial developments could significantly affect a single industry or group of related industries.

• Prepayment. The ability of an issuer of a debt security to repay principal prior to a security’s maturity can cause greater price volatility if interest rates change.

• Issuer-Specific Changes. The value of an individual security or particular type of security can be more volatile than, and can perform differently from, the market as a whole. A decline in the credit quality of an issuer or a provider of credit support or a maturity-shortening structure for a security can cause the price of a security to decrease. Lower-quality debt securities (those of less than investment-grade quality, also referred to as high yield debt securities or junk bonds) involve greater risk of default or price changes due to changes in the credit quality of the issuer. The value of lower-quality debt securities can be more volatile due to increased sensitivity to adverse issuer, political, regulatory, market, or economic developments.

• Correlation to Index. The performance of an underlying index fund and its index may vary somewhat due to factors such as fees and expenses of the underlying fund, transaction costs, sample selection, regulatory restrictions, and timing differences associated with additions to and deletions from the index.

benchmark index. As a result, an underlying fund’s performance could be lower than actively managed funds that may shift their portfolio assets to take advantage of market opportunities or lessen the impact of a market decline or a decline in the value of one or more issuers.

• Leverage Risk. Leverage can increase market exposure, magnify investment risks, and cause losses to be realized more quickly.

• Inflation-Protected Debt Exposure. Increases in real interest rates can cause the price of inflation-protected debt securities to decrease. Interest payments on inflation-protected debt securities can be unpredictable.

An investment in the fund is not a deposit of a bank and is not insured or guaranteed by the Federal Deposit Insurance Corporation or any other government agency. You could lose money by investing in the fund.

Performance history will be available for the fund after the fund has been in operation for one calendar year.

FMR Co., Inc. (the Adviser), an affiliate of Fidelity Management & Research Company (FMR), is the fund’s manager.

Andrew Dierdorf (co-manager) and Brett Sumsion (co-manager) have managed the fund since August 2018.

You may buy or sell shares through a Fidelity^® brokerage or mutual fund account, through a retirement account, or through an investment professional. You may buy or sell shares in various ways:

The price to buy one share is its net asset value per share (NAV). Shares will be bought at the NAV next calculated after an order is received in proper form.

The price to sell one share is its NAV. Shares will be sold at the NAV next calculated after an order is received in proper form.

The fund is open for business each day the New York Stock Exchange (NYSE) is open.

Distributions you receive from the fund are subject to federal income tax and generally will be taxed as ordinary income or capital gains, and may also be subject to state or local taxes, unless you are investing through a tax-advantaged retirement account (in which case you may be taxed later, upon withdrawal of your investment from such account).

The fund, the Adviser, Fidelity Distributors Corporation (FDC), and/or their affiliates may pay intermediaries, which may include banks, broker-dealers, retirement plan sponsors, administrators, or service-providers (who may be affiliated with the Adviser or FDC), for the sale of fund shares and related services. These payments may create a conflict of interest by influencing your intermediary and your investment professional to recommend the fund over another investment. Ask your investment professional or visit your intermediary’s web site for more information.

The fund seeks high total return until its target retirement date. Thereafter the fund’s objective will be to seek high current income and, as a secondary objective, capital appreciation.

The following table describes the fees and expenses that may be incurred when you buy and hold shares of the fund.

This example helps compare the cost of investing in the fund with the cost of investing in other funds.

• Allocating assets according to a neutral asset allocation strategy shown in the glide path below that adjusts over time until it reaches an allocation similar to that of the Fidelity Freedom^® Blend Income Fund, approximately 10 to 19 years after the year 2005. FMR Co., Inc. (the Adviser) may modify the fund’s neutral asset allocations from time to time when in the interests of shareholders.

• Buying and selling futures contracts (both long and short positions) in an effort to manage cash flows efficiently, remain fully invested, or facilitate asset allocation.

• The Adviser may continue to seek high total return for several years beyond the fund’s target retirement date in an effort to achieve the fund’s overall investment objective.

• Designed for investors who retired in or within a few years of 2005 (target retirement date) at or around age 65.

• Interest Rate Changes. Interest rate increases can cause the price of a debt or money market security to decrease.

• Industry Exposure. Market conditions, interest rates, and economic, regulatory, or financial developments could significantly affect a single industry or group of related industries.

• Prepayment. The ability of an issuer of a debt security to repay principal prior to a security’s maturity can cause greater price volatility if interest rates change.

• Issuer-Specific Changes. The value of an individual security or particular type of security can be more volatile than, and can perform differently from, the market as a whole. A decline in the credit quality of an issuer or a provider of credit support or a maturity-shortening structure for a security can cause the price of a security to decrease. Lower-quality debt securities (those of less than investment-grade quality, also referred to as high yield debt securities or junk bonds) involve greater risk of default or price changes due to changes in the credit quality of the issuer. The value of lower-quality debt securities can be more volatile due to increased sensitivity to adverse issuer, political, regulatory, market, or economic developments.

of the actual securities included in the index. This differs from an actively managed fund, which typically seeks to outperform a benchmark index. As a result, an underlying fund’s performance could be lower than actively managed funds that may shift their portfolio assets to take advantage of market opportunities or lessen the impact of a market decline or a decline in the value of one or more issuers.

• Leverage Risk. Leverage can increase market exposure, magnify investment risks, and cause losses to be realized more quickly.

• “Value” Investing. “Value” stocks can perform differently from the market as a whole and other types of stocks and can continue to be undervalued by the market for long periods of time.